Electronic devices include a board on which semiconductor elements such as IC chips and capacitors are mounted.
Recently, electronic devices are downsized or high-functionalized, and therefore the number of the semiconductor elements to be mounted on a single board increases. This causes a problem that a sufficient mounting area of the semiconductor elements cannot be secured.
In order to solve such a problem, an attempt is made to secure a mounting area of semiconductor elements by embedding them into a semiconductor element mounting board (multilayer wiring board) so that an electronic device can be downsized (see, for example, patent document 1).
However, in the semiconductor element mounting board into which semiconductor elements are embedded, structures of upper and lower sides thereof become unsymmetric, and physical properties thereof also become unsymmetric. Because of this, there is a problem in that warpage is likely to occur in the board, so that reliability of the semiconductor element mounting board is lowered.    Patent document 1: JP-A 2005-236039